This invention relates to a radial tire for aircraft.
A radial tire for aircraft has been known as disclosed in Japanese patent application laid-open No. 57-201,704. The tire includes a toroidal carcass layer consisting of at least one carcass ply having cords embedded therein extending perpendicular to an equatorial plane of the tire, a tread rubber arranged radially outwardly of the carcass layer, and a breaker arranged between the carcass layer and the tread rubber and formed by laminating at least one layer of circumferential plies and at least one layer of a breaker ply. Each of the circumferential plies has cords embedded therein substantially parallel to the equatorial plane. On the other hand, the breaker ply has cords embedded therein and intersecting at angles of 10.degree.-70.degree. with respect to the equatorial plane.
In general, a radial tire for aircraft is often damaged to a depth arriving at breaker layers by stones, metal pieces and the like when rolling. If the circumferential plies as above described are arranged on an outermost layer of the breaker layer, the cords embedded in the circumferential ply will be broken.
In this case, extending directions of the circumferential plies are substantially same as rotating directions of the tire. Therefore, when the cords are broken as above described, the cords and tread rubber are readily peeled from the broken positions and such peeling will rapidly develop in circumferential directions until the cords and the tread rubber are dislodged from the tire and fly in all directions, which is so-called "peel-off". Once such a peel-off occurs, fragments of the cords and the tread rubber impinge against a body of the aircraft at high speeds to damage it. Therefore, safety for the aircraft could not be ensured, while expensive and time-consuming repairing of the aircraft is required.
In order to avoid this, the tire disclosed in the above Japanese application includes a breaker ply arranged radially outwardly of the circumferential plies to prevent the peeling of the cords of the circumferential plies and the tread rubber developing in the circumferential directions when damaged. With the tire disclosed in the Japanese application, moreover, the cords of the breaker ply are oblique to the tire equatorial plane so that when the tire is injured and one oblique cord is cut, the cut growing in a circumferential direction will encounter adjacent oblique cords which would obstruct the growth of the cut. Therefore, peel-off can be prevented by such cords oblique to the equatorial plane of this tire.
With such a radial tire for an aircraft, however, as shoulders of the tire are dragged on a road when rolling, only the shoulders are rapidly worn off to cause irregular wear. The reason will be explained hereinafter.
In general, a tire is subjected to bending deformation at contacting portions with a road when rolling as shown in FIG. 9. If a belt layer consists of only breaker ply of a plurality of layers, the tire will undergo the following stresses. The farther radially inwardly from a neutral plane in a center of the belt layer or the nearer to the carcass layer, the larger tensile stresses occur. On the other hand, the farther radially outwardly from the neutral plane or the nearer to the tread rubber, the larger compressive stresses occur.
With the hitherto used tire as above described, since the circumferential plies arranged radially inwardly of the breaker ply or near to the carcass layer are subjected to the large tensile stresses, elongation and contraction of the belt layer itself are considerably obstructed. The result is that difference in circumferential length between the tread center and shoulder owing to crown curvatures (curvatures of tread contours in meridian sections) cannot be taken up only by the elongation of the belt layer when contacting a road.
Therefore, the difference in the circumferential length is accumulated in the tread rubber of the shoulders from initial contacting to leaving the road to increase the shearing deformations in the circumferential directions. However, such shearing deformations are rapidly restored when the tread rubber leaves the road so that the tread rubber at the shoulders drags on the road.
Moreover, a radial tire for an aircraft has been known as disclosed in Japanese patent application laid-open No. 61-57,406. This tire includes a toroidal carcass layer consisting of at least one carcass ply having cords embedded therein intersecting at angles of 60.degree.-90.degree. with respect to an equatorial plane of the tire, a tread rubber arranged radially outwardly of the carcass layer, and a belt layer arranged between the carcass layer and the tread rubber and made of a lamination of at least one circumferential ply and at least one breaker ply. The circumferential ply has cords made of organic fibers such as nylon embedded therein and substantially in parallel with the equatorial plane. On the other hand, the breaker ply has cords made of organic fibers embedded therein and intersecting at angles less than 30.degree. with respect to the equatorial plane.
At least one breaker ply has a width (before being folded) wider than those of the other breaker plies and circumferential plies, and width edges of the breaker ply extending laterally from the other belt and circumferential plies are folded radially outwardly or radially inwardly onto the same side. As an alternative, one width edge may be folded radially outwardly and the other width edge may be folded radially inwardly. As a result, the folded width edges of the breaker ply are on the center thereof extending from one folded width edge to the other folded width edge. In this case, the width of the breaker ply after being folded (ply width) is substantially equal to those of the other belt and circumferential plies.
With such a breaker ply, particularly a folded breaker ply, since the cords embedded therein are made of heat-shrinkable organic fibers, they will shrink several percent in longitudinal directions by vulcanizing heat in vulcanizing. When they shrink, the width of the breaker ply 33 (ply width) is reduced to the positions in phantom lines as shown in FIGS. 1 and 2 because of the cords 31 extending obliquely with respect to the equatorial plane 32 shown in the drawings.
In this case, if the width edges A and B of the breaker ply 33 and hence the cords 31 embedded therein have been folded as above described, the cords 31 at the folded ends 34 and 35 are displaced in width directions of the breaker ply 33 (axial directions of the tire) by a restraining action of the cords 31 (inclined in reverse directions of the cords at the width center of the ply) of the folded width edges A and B. An influence by such a restraining action is maximum at the folded ends 34 and 35 and becomes smaller when approaching the center of the ply.
As a result, as illustrated in FIG. 2 intersecting angles a of the cords 31 with respect to the equatorial plane 32 change as shown in broken lines and become smaller as approaching the folded ends 34 and 35. Therefore, distances L between the cords 31 in the proximity of the folded ends 34 and 35 become narrower than those M before vulcanizing. In this case, the cords 31 embedded in the width center C of the breaker ply 33 continuously extend from one folded end to the other folded end so that the influence of the shrinkage of the cords 31 in all the areas concentrates on the center of the breaker ply 33, with the result that the reduction in width (ply width) at the center C in vulcanizing is enhanced. Moreover, such a reduction in ply width is converted into a reduction in intersecting angles a in the proximity of the folded ends 34 and 35 so that the distance L between the cords 31 in the proximity of the folded ends 34 and 35 become much narrower.
When the tire is deformed in contacting a road, the rubber between the cords 31 is subjected to shearing forces. Such shearing forces become larger as approaching the folded ends 34 and 35 whose distances L between the cords are narrower. Therefore, the rubber between the cords 31 in the proximity of the folded ends 34 and 35 is subjected to great shearing strains so that separations at belt ends are likely to occur.
In pneumatic tires for aircraft, the application of radial carcasses has been strongly studied and developed. However, owing to excessive side forces particularly in such a use, rubber cracks similar to chevron-cuts often occur in buttresses of the tires.
In Japanese utility model application laid-open No. 63-121,102, it is proposed to provide hollow portions having several mm depth and widths wider than the depths in the buttresses in order to prevent separations of belt layers at shoulders to improve the durability of the radial tire for aircraft. However, this Japanese specification does not suggest avoiding the rubber cracks in buttresses. There has been no documents mentioning the relations between the rubber cracks in buttresses and strong side forces acting upon tires due to strong traverse wind when landing.